Gluconeogenesis is the metabolic pathway for the biosynthesis of glucose from non-carbohydrate precursors including pyruvate, lactate, and citric acid cycle intermedates. This pathway occurs predominantly in the liver and to a lesser extent in the kidney and is triggered by a fall in blood glucose concentration. Gluconeogenesis meets the needs of the body for glucose when there is insufficient intake of carbohydrates in the diet. It is also critical to the maintenance of a continuous energy supply, in the form of glucose, to red blood cells and tissues of the central nervous system, which do not undergo gluconeogenesis. In addition, gluconeogenesis represents a mechanism by which products of metabolism from other tissues are cleared from the blood and converted back into glucose. Under fasting conditions glucose production through this pathway maintains the basal glucose concentrations necessary to sustain primary physiologic functions. The gluconeogenic pathway is essentially glycolysis (the breakdown of glucose received predominantly from the diet) in reverse. There are four enzymes necessary to bypass the thermodynamically unfavorable steps of glycolysis. These enzymes are pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase. The rate-limiting step of gluconeogenesis is catalyzed by phosphoenolpyruvate carboxykinase and this enzyme has been well characterized in several species. Two forms (isozymes) of the enzyme have been isolated and the total enzyme activity displayed in humans is equally divided between the cytosolic and mitochondrial forms (Hanson and Patel, Adv. Enzymol. Relat. Areas Mol. Biol., 1994, 69, 203-281).
Mitochondrial phosphoenolpyruvate carboxykinase (also known as PEPCK-mitochondrial, PEPCK-M, PCK2 and mtPEPCK) is expressed in a variety of human tissues, mainly the liver, kidney, pancreas, intestine and fibroblasts (Modaressi et al., Biochem. J., 1998, 333, 359-366; Modaressi et al., Biochem. J., 1996, 315, 807-814). PEPCK-mitochondrial deficiency, while not well documented, has been associated with failure to thrive, hypoglycemia and liver abnormalities. Unlike the cytosolic form (PEPCK-C), the mitochondrial form (PEPCK-mitochondrial) is expressed constitutively and is not regulated by hormonal stimuli (Hanson and Patel, Adv. Enzymol. Relat. Areas Mol. Biol., 1994, 69, 203-281). In addition, the two forms are located on separate chromosomes with localized to chromosome 14q11 (Modaressi et al., Biochem. J., 1998, 333, 359-366) and PEPCK-C residing on chromosome 20q11 (Stoffel et al., Hum. Mol. Genet., 1993, 2, 1-4). This fact, in conjunction with the differential regulation and expression of the two forms has led to the suggestion that the role of PEPCK-mitochondrial may not be purely gluconeogenic. For example, PEPCK-mitochondrial is found in non-gluconeogenic fibroblasts where it may act in the process of replenishing the citrate cycle (Modaressi et al., Biochem. J., 1998, 333, 359-366). It has also been shown to be the only isoform expressed in hepatoma cells (Modaressi et al., Biochem. J., 1998, 333, 359-366).
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of PEPCK-mitochondrial. Consequently, there remains a long felt need for agents capable of effectively inhibiting PEPCK-mitochondrial function.
Antisense technology is emerging as an effective means for reducing the expression of specific gene products and may therefore prove to be uniquely useful in a number of therapeutic, diagnostic, and research applications for the modulation of PEPCK-mitochondrial expression.